LinkedIn previews are flaky - let's rule out IPv6 misconfig

[refset]

IPv6 is failing:

• IPv6: 2a05:d014:58f:6200::259, 2a05:d014:58f:6200::258
• Immediate connect fail for 2a05:d014:58f:6200::259: Network is unreachable

LinkedIn's crawlers might be trying to connect via IPv6 first, and if Netlify's IPv6 endpoints
are having issues or are misconfigured, LinkedIn gets "Network is unreachable" and reports it as
a connection error.

My machine then falls back to IPv4 and succeeds, but LinkedIn's crawler might not be handling the
IPv6 failure gracefully.

This is a Netlify/DNS infrastructure issue, not something in your code.

1. Check your DNS settings - If you're managing DNS yourself, you might have AAAA records
   pointing to problematic IPv6 addresses
2. Disable IPv6 temporarily - Remove AAAA records from your DNS if possible (not ideal long-term)

In the meantime, this explains the intermittent nature - LinkedIn's crawlers hitting IPv6 fail,
while IPv4 requests succeed.